Conventionally, various materials have been provided as a radiation shielding material for reducing the amount of radiation from a substance that emits radiation such as a gas, a liquid, and a solid (hereinafter, collectively referred to as radioactive substances in some cases), and a typical material thereof is lead. However, although lead has an excellent radiation shielding effect, the lead itself has a poor workability and the use range of lead is limited, e.g., it is used by being embedded in a wall of a simple structure such as a box in a plate-like material form. Further, also lead glass has a high radiation shielding effect but is brittle because it is glass. In addition, it is heavy. Therefore, the use range of lead glass is limited similarly to lead.
As compared with the above-mentioned lead or lead glass, a radiation shielding material obtained by filling resin with powder having a radiation absorbing effect has a lower shielding effect. However, because the radiation shielding material is light and can be molded in various shapes, it is expected as a material that can be processed into a structure such as a vessel, a pipe, a protector, and a syringe.
For example, a radiation shielding material obtained by filling resin with metal powder such as lead and tungsten and a compound such as barium sulfate is provided (see Patent Literatures 1 to 3).
However, the above-mentioned metal-based radiation shielding material has such a problem that the material becomes heavier when the filling amount is increased to improve the radiation shielding effect. Furthermore, because lead is a toxic substance, such a problem that use of lead is being limited occurs.
Meanwhile, because the compound-based filler such as barium sulfate is relatively light and has a certain level of radiation shielding effect, it is favorably used.
Meanwhile, the conventionally-proposed radiation shielding material is a non-transparent material except for the lead glass, and just has to be used at the expense of transparency that is necessary to check the content to be shielded its radiation.
Further, as a transparent resin material for radiographic visualization in the field of dentistry, also those obtained by filling nanoparticles smaller than a wavelength of visible light have been proposed (see Patent Literature 4). However, the nanoparticles are difficult to disperse in filling, and a sufficient amount of nanoparticles cannot be filled. Therefore, it is difficult to achieve a sufficient shielding effect and such a problem that the transparency is significantly reduced when the filling amount is increased may occur.
Patent Document 1: Japanese Patent Application Laid-open No. 2007-212304
Patent Document 2: Japanese Patent Application Laid-open No. 2013-127021
Patent Document 3: Japanese Patent Application Laid-open No. 2013-181793
Patent Document 4: Japanese Patent Application Laid-open No. 1986-176508